Here is the full list of all 45 The Forest achievements. It takes around 50-60 hours to unlock all of the achievements on Windows.
Build a super long wall
Pass 50,000 steps
Eat all mushroom types
Set off 20 bombs
Kill all animal types and display heads
Kill 6 or more fish with a stick of dynamite. Alone in Single Player or together in Multiplayer.
Repair a shelter
Find all missing passengers
Kill shark. Alone in Single Player or together in Multiplayer.
Explore all caves
Collect all cassette tapes!
Collect all robot pieces
Knock down 6 or more trees with 1 explosive. Alone in Single Player or together in Multiplayer.
Craft 10 medicine items
Sleep on yacht
Craft all items
Grow all plant types
Make and wear stealth armour
Cut down 100 trees
Catch fish with a trap. Alone in Single Player or together in Multiplayer.
In Single Player, don't kill any cannibals for more than 10 days in a row
Survive 5 nights
Kill a bunny. Alone in Single Player or together in Multiplayer.
Kill bird with arrow
Survive 1 night
Use the compass
Eat an enemy
Eat an entire family
Share a food or drink item in MP
Share a weapon in MP
Play through entire game without killing or eating animals. Alone in Single Player or together in Multiplayer.
Revive one co-op player
Revive 10 co-op players
Sleep with another player (group sleep)
Killed downed enemy with rock
Chop up 50 bodies
Finish Game
In Single Player, kill 100 cannibals
Cut down 1000 trees